Oil refining process



Aug. 1-9, 1941.l

R. E. DALY ETAL OIL REFINING PROCESS Filed April 16, 1938 TEM/2 125-140W- fxcfss Huffm=15f4070 TIME.- .50-60 M/Ms.

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ATTO R N EY Patented Aug. i9, 1941 OIL REFINING PROCESS Raymond E; Dalyand James ,F. Walsh, Chicago,

Ill.,

assignors to American Maize-Products Company, a corporation of MaineApplication April 16, 1938, Serial No. 202,462

(ci. 26o-425) s claims.

Our invention relates to the refining of vegetable oils and moreparticularly to a process of producing a high yield of refined corn oilof relatively low fatty acid content.

In the old, well-known processes for refining of vegetable oils such ascorn oil, cotton-seed oil and the like, it has been customary to treatbatches of the settled crude oi1.with a large excess of alkali whilewarm for the purpose of neutralizing the free fatty acids present inthis oil. This neutralizing treatment, which results in the formation ofsoap stock commonly referred to as foots, is usually continued for aconsiderable period of time, for example, several hours. This prolongedcontacting of the oil with large amounts of alkali also causessaponification of some of the neutral oil with formation of soapresulting in loss of this amount of oil, which is known as a refining orsaponification loss.

After the neutralizingtreatment the foots or soap stock formed, byreaction of the alkali on the fatty acids and part of the neutral oil,is allowed to settle along with the caustic solution.

ments have been made upon the above described prior art process, namely,in the nature of a quick continuous process by means of which largeryields of neutral oil are obtained, that is, the saponification loss isreduced somewhat and vless neutral oil` remains in the soap stock.

Although the yield has been improved in this manner, the final oilproduct obtained by this process is not of as good quality as the oilobtained by the older refining processes. The oil produced by theserecent processes does not fully meet the presentmarket requirements,particularly because its fatty acid content is higher than thatgenerally desired and obtainable through 'the prior conventionalprocedures. One of the principal reasons for this disadvantage andcommercial limitation is that in this recent quick, continuous processthe oil and caustic are maintained in contact for a very short periodofv time, and although greater amounts of alkali are used to compensatefor the shortened time of reaction between the oil and alkali, there isnot sufficient opportunity for the alkali to neutralize all or thedesired maximum amount of the free fatty acids present in the crude oil.Accordingly, an undesirable relatively large amount of free fatty acidsremain in the final product.

In accordance with our present invention we have discovered a processfor refining corn oil and the like by means of which the advantages ofboththe prior and more recent improved reriining processes can beobtained and the dis-v 1 advantages of those processes avoided. Morerelatively small amount of alkali for a period of time intermediate thatemployed in the above described processes, and then subjecting thisFtreated oil to centrifugal action to separate the soap stock from theneutral oil, the latter will be produced in relatively high yields andof a quality that meets the present commercial requirements. Thisprocess comprises generallyy reacting the crude oil with approximately15% to 40% excess alkali for a period of time of about 30 to minutes andat a temperature between about F. to 140 F. to effect maximumneutralization of the free fatty acids present, and at the same timeproduce a minimum loss of oil by saponication of the neutral oil by thealkali. After this neutralization ltreatment for a period of aboutone-half hour to one hour, the treated mixture is passed through acentrifuge in which the soap stock is separated from the neutral oil.The neutral oil is then advantageously subjected to a chillingoperation, and if necessary, is filtered in the presence of filter-aidto remove the remaining small amounts of alkali, water and the like.After this treatment the oil is bleached, deodorized and otherwiserefined in conventional manner.

As an alternative to the above process, we have found it advantageous insome instances, depending somewhat upon the percentage of impurity ofthe crude oil, to partially refine this oil preliminarily to' theneutralization treatment. One advantage of this preliminary refiningtreatment is that the lecithin content of the oil may be isolated foruse, whereas if the oil is neutralized immediately, the lecithincontentI is lost.

The method of operation of our invention may be easily understood fromthe following more detaileddescription taken in conjunction with theaccompanying drawing in which the single figure represents a' flowdiagram of our process with alternatives.

Referring now tothe drawing-the crude corn oil or other similarvegetable oils, may be sub- :lected directly to the neutralizingtreatment with alkali as indicated, orit may be first partially refinedas shown in this flow diagram, by treating the crude oil with sodiumferrocyanide. The amount of ferrocyanide used may be varied from about0.1% to 0.5% by weight of the oil, and we have found it practical to addto the oil an amount equal to about 0.2%- of the weight of the oil; orwe may add, based on the weight of the oil, about 2% of a 10% solutionof the ferrocyanide. This treatment with ferrocyanide is carried out atroom temperature until a break is obtained, that is, until it isapparent that the treatment has caused some of the fatty acids and otherimpurities to coagulate.

Following the treatment with sodium ferrocyanide the treated oil isfiltered, preferably in the presence of a small amount of filter-aid,such as diatomaceous earth or filter cel, to separate the coagulatedmaterial from the partially refined oil. The residue produced by thisfiltration contains a mixture of lecithin and oil, from which thelecithin may be isolated in any suitable conventional manner. Thepartially refined oil resulting from this treatment with the sodiumferrocyanide has its original acidity reduced to an extent of about 30%to 60% and a similar reduction in the color of the oil also takes place.

The partially refined oil, or the crude oil, if the sodium. ferrocyanidetreatment has not been used, is divided into several batch, such asindicated by the three spaces in the flW diagram. Each of these batchesof oil is now heated to a temperature of about 125 F. to about 140 F., apreferred temperature being about 126 F. and a suitable alkali such ascaustic soda is added to each batch of oil. The alkali is added in anamount of about 15% to 40% excess of that theoretically required toneutralize the free fatty acids present in the oil. An advantageousexcess is about 25%. This netralizing operation is carried on for about30 to 60 minutes, and prefere ably about 45 minutes. If desired, each ofthe batches is agitated during this treatment.

After the completion of the neutralizing treatment, the oil andresulting soap stock from each batch is fed into a centrifuge orcentrifuges. The size of each batch of oil is regulated so as to supplythe centrifuge for about 30 to 60 minutes time. In the centrifuge thesoap stock is separated from the neutral oil and this oil. is passed onto the other refining steps, including chilling, bleaching anddeodorizing.

One of the purposes of the chilling operation ls to enable removal fromthe neutralized oil of the small traces of caustic liquor that remainentrained in the oil. These amounts of caustic are extremely small andcannot be removed readily by ltration of the oil. We have found however,that if the neutralized oil is chilled, these impurities will be thrownout of solution and can then be removed by filtration if small amountsof filter cel or diatomaceous earth are added. This method of removal wehave found is more effective than the method heretofore proposed, ofwashing lthe neutralized oil with hot water. The chilling of theneutralized pil to eect separation from the traces of caustic can beeffected by any suitable means such as for example, by a pipe heatinterchanger through which the oil is caused to pass, and itstemperature reduced to below about 60v F. The filter aid with adsorbedimpurities can be removed from the neutralized oil by means of a filter-press or a hollow barreltype of centrifuge commonly used for removing-small amounts of solid sludges continuously.

'I'he final steps of decolorizing, drying. deodorizing, etc. maybecarried out according to any of `the conventional; procedures wellknown in this field.

As a specific, but non-limiting example of the process of our inventiongenerally described above, We have treated 500 pounds of crude oilhaving a 1.7% content of free fatty acid content, with 12.3 pounds of 17B. caustic soda to effect the desired neutralization of the free fattyacids. During this treatment the oil and caustic mixture was heated toabout 125 F. for a period of about one hour. As a result of thistreatment the usual break" occurred and the appliedheating was thenremoved. During this treatment the oil and caustic mixture wasagitated.4 After centrifuging the thus treated oil to separate the soapstock from the neutralized oil the neutralized oil was then chilled toabout 60 F. and passed into a mixing tank where approximately one poundof filter cel was added, and the neutralized oil finally separated byfilter pressing.

The neutralized loil resulting from the above described process of ourinvention has a free fatty acid content of less than 0.008%. Thispercentage shows an advantage over the oil prepared by the recentlyproposed quick, continuous processes, which ranges from about 0.015% to0.04%. While this decrease in free fatty acid content appears to besmall, in practice, it represents the difference between a commerciallysatisfactory and other words, the trade has demanded an oil having afree fatty acid content of less than that normally contained in theproduct resulting from the quick, continuous type of process, namelyabout 0.04% or slightly less. In addition to obtaining a product ofbetter quality the process of our invention provides as good or betteryields than those obtained in the quick, continuous processes. Forexample, the neutral oil contained in the foots produced in our processgenerally runs from 15 to 25% of the total fatty acids, which iscomparatively small and accordingly effects a substantial increase inthe yield of the finally refined oil.

The process of our invention, by using a smaller excess of alkali andcompensating for this reduction by increasing to a limited extent thetime of reaction of the alkali and crude oil, effects a substantialreduction in the refining loss. Our process produces an improved oil ofrelatively low fatty acid content and obtains yields of refined oilequal to or slightly better than the quick refining process. In additionto the improvements the process effects a substantial saving in theamount and cost of alkali used as illustrated by the following:

For a crude oil of an acidity of 1.4% the theoretical amount of alkalias sodium hydroxide necessary to neutralize this free acidity is equalto one-seventh times the free acid or .2 pound sodium hydroxide perpounds of oil. In our proposed process we use a maximum of 40% excesswhich for this oil would mean a maximum excess of .08 pound or a totalof .28 pound, which includes the 40% excess. The same crude oil of 1.4%acidity refined by the quick continuous reunsatisfactory product. In ying said neutralized oil to remove the soap stock tralize the free fattyacid. Thus, by comparison, it is apparent that our 15% to 40% excessalkali results in a considerable saving of alkali and thereby materiallyreduces the refining cost.

Various modifications and changes may be made in our process asdescribed hereinbefore without departing from the scope of ourinvention.

We claim:

1. The process of refining crude corn oil comprising treating said oilwith sodium ferrocyanide to effect partial neutralization of the freeVfatty acid content of said oil, adding filter-aid and filtering toremove the 'coagulated material, neutralizing the partially refined oilin batches by the addition of approximately 15% to 40% excess alkaliwhile heating to a temperature of approximately 125 F. to 140 F. forabout 30 to 60 min-4 utes, combining the neutralized oil from saidbatches, centrifuging said neutralized oil to remove the soap stockformed by neutralization of the free fatty acids, chilling theneutralized oil to separate out of solution remaining small traces ofalkali and water, adding filter-aid and ltering.

2. The process of refining crude corn oil comprising treating said oilwith about 0.2% soformed by neutralization of the free fatty acids.

3. A process of reflningcorn oil comprising adding to said oil about 2%of a 10% solution of sodium ferrocyanide, maintaining said ferrocyanidein contact with said oil until a coagulum is formed, filtering to removesaid coagulum thereby producing a partially refined corn oil, separatingsaid partially refined corn oil into batches, treating each of saidbatches of oil at a temperature of approximately 125 F. to 140 F. forabout 30 to 60 minutes with a 15% to 40% excess of alkali to effectneutralization of the remaining free fatty acid content of said oil,centrifuging the neutralized oil mixture to effect separation of theneutralized oil from the soap stock form ed by the reaction between saidalkali and the free fatty acids in said oil, chilling,

l bleaching and deodorizing said neutralized oil.

.4. In the refining of vegetable oil'containing free fatty acids,thelmethod which comprises treating the oil with sodium ferrocyanide, todecrease the acidity, then treating the oil with an alkali to neutralizeadditional acid and form soap, and separating the soap from theremaining oil. 5. In the refining of vegetable oil containing lecithinand free fatty acids, the method which comprises treating the oil withan aqueous solution of sodium ferrocyanide to cause coagulation oflecithin and a part of the fatty acids, separating the coagulatedmaterials from the oil, treating the remaining oil with alkali toneutralize additional acid and form soap. and separating the soap fromthe alkali-treated oil.

RAYMOND E. DALY. JAMES F. WALSH.

